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Home >> Chevrolet >> 2005 >> Uplander Base, Van Cargo Extended >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Computer/Integrating Systems) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Low Speed GMLAN Device >> Test Description
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Test Description

WARNING: This page is about a different car, the 2005 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  A partial malfunction in the low speed GMLAN serial data circuits uses a different procedure from a total malfunction of the low speed GMLAN data circuits. Refer to Data Link References  to identify which modules communicate on the low speed GMLAN serial data circuits.
  2. 3:  The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.
  3. 7:  Data link connector terminal 1 provides the connection to the GMLAN serial data low circuit and the GMLAN serial data low circuit respectively.
  4. 16:  The communication malfunction may have prevented diagnosis of the customer complaint.
Scan Tool Does Not Communicate with Low Speed GMLAN Device

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List in Wiring Systems
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2 
IMPORTANT: Make sure the CANdi module is not malfunctioning. When functioning properly, the CANdi module LED will be flashing. In the event of a problem, the LED will be continually illuminated.
  1. Turn ON the ignition, with the engine OFF.
  2. Perform the Vehicle DTC Information function on the scan tool, under Computer/Integrating Systems.
Does the scan tool communicate with any module on the low speed GMLAN serial data circuit?		 Go to Step 3  Go to Step 5 
3  Did you record any DTCs in the range of U2105 to U2177? Go to DTC U2105-U2199  Go to Step 4 
4
IMPORTANT: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.
Test the low speed GMLAN serial data circuits for:
  • An intermittent short to ground
  • An intermittent short to voltage
  • An intermittent open
Refer to the following procedures in Wiring Systems:Did you find and correct the condition?		 Go to Step 18  Go to Diagnostic Aids
5 Test the following circuits of the body control module (BCM) for an open or short to ground:
  • The battery positive voltage input circuits
  • The battery positive voltage output circuits
  • The ignition mode switch input circuits
  • The switched battery positive voltage circuits

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 15  Go to Step 6 
6 Test the ground circuits of the BCM for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 15  Go to Step 7 
7 
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor a connection at the DLC terminal 1. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Diagnostic System Check - Vehicle in Vehicle DTC Information Go to Step 8 
8
  1. Disconnect the farthest module from the DLC that is connected to low speed GMLAN serial data circuit. Refer to Data Link Connector (DLC) Schematics .
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?		 Go to Step 13  Go to Step 9 
9
  1. Turn OFF the ignition.
  2. Disconnect the farthest module from the DLC that is still connected to low speed GMLAN serial data circuit. Refer to Data Link Connector (DLC) Schematics .
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?		 Go to Step 10  Go to Step 11 
10 Test the low speed GMLAN serial data circuit between the last two disconnected modules for:
  • A short to ground
  • A short to battery

Did you find and correct the condition?		 Go to Step 15  Go to Step 13 
11 Is the BCM the last module still connected to low speed GMLAN data circuit? Go to Step 12  Go to Step 9 
12
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the low speed GMLAN serial data circuit between BCM and the previous disconnected module and between BCM and DLC for:
    • A short to ground
    • A short to battery
    • An open
Did you find and correct the condition?		 Go to Step 15  Go to Step 13 
13 Inspect for poor connections at the low speed GMLAN serial data circuit of the last disconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 15  Go to Step 14 
14
IMPORTANT: Perform the module setup procedure if required.
Replace the last disconnected module. Refer to Control Module References  for the appropriate repair instructions.Did you complete the replacement?		 Go to Step 15  -
15
  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Wait for 10 seconds.

    The scan tool may require a power up reset before communication will occur due to a short on the low speed GMLAN serial data circuits. Turn OFF or disconnect the scan tool prior to performing this test.

  5. Select the Display DTCs function for each module.
  6. Record all of the displayed DTCs and the DTC status.
Did you record any DTCs which begin with a "U" and with a current status?		 Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information Go to Step 16 
16  Did you record any DTCs which do not begin with a "U"? Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information Go to Step 17 
17 Did you diagnose all of the DTCs? Go to Step 18  Go to Step 15 
18 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
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